Support changing verbosity on-the-fly

[itslychee]

Let the user change the output of the program (e.g. Nix substitution logs, you get it) without needing to quit and add -v to the program

[mrshmllow]

Shouldn't be too hard. I actually love this idea

[itslychee]

Let the user change the output of the program (e.g. Nix substitution logs, you get it) without needing to quit and add -v to the program

program verbosity is of course feasible but substitution is not, but I guess the program can mask it? so that's probably not an issue!